The present invention relates to systems and methods for micromachining holes in objects such as electrical circuits, and, more particularly, to laser micromachining systems and methods which employ various laser sources simultaneously outputting more than one wavelength.
It is known to use lasers to micromachine holes such as vias, micro vias, and blind micro vias, in electrical circuits such as printed circuit boards and interconnect chip packages.
Various materials forming electrical circuits react differently to laser beams in different spectral ranges. For example, various materials used in the manufacture of printed circuit boards have different power and energy requirements for removal by thermal interaction or ablation.
Generating a suitable laser beam driver for use in a laser micromachining system, such as a laser drill, includes generating a pulsed laser beam from a diode-pumped frequency-modified solid state laser. Typically, frequency modification, sometimes referred to as frequency conversion, is achieved by passing the beam through at least one non-linear crystal to generate one or more harmonics. All but one of the harmonic components are removed from the frequency-modified beam and discarded so as to result in a beam having a single desired wavelength.
A general aspect of the present invention relates to systems for improving the utilization of laser energy produced by frequency modified lasers, in the context of laser micromachining systems. A typical application for laser micromachining systems is drilling holes on electrical circuits, however the systems and methodologies described hereinbelow may be employed in any suitable laser machining and micromachining application.
One embodiment of the present invention relates to a laser micromachining system employing a pulsed laser which outputs a frequency modified laser beam having at least two spectral components. As used herein, a frequency modified, or frequency converted, laser beam means a laser beam whose spectral composition is modified by any suitable means to result in a laser beam having a different single wavelength component, or to have several wavelength components, for example by harmonic generation. Such a frequency modified laser beam optionally includes the fundamental wavelength component of an initially input laser beam.
Another embodiment of the invention relates to a method of laser micromachining employing a first pulse defined by a first spectral component, and then a second pulse defined by a second spectral component, each delivered to the same region of an object to be micro-machined.
Still another embodiment of the invention relates to a method of laser micromachining employing time-altered pulses. A time-altered pulse is a pulse formed of at least two pulse components in which at least one of the pulse components is time delayed such that the pulse duration and/or the time separation between the two pulse components is altered with respect to an initial pulse or sequence of pulses. The pulse components forming a time altered pulse are from different wavelength components. Optionally, they are from the same wavelength component.
The invention is taught below by way of various specific exemplary embodiments explained in detail, and illustrated in the enclosed drawing figures.